Method for curing resin with ultrasound

ABSTRACT

A method for curing a resin includes the steps of placing the resin into a reaction vessel, drawing a vacuum in the reaction vessel, positioning the reaction vessel in a gaseous coupling fluid, and applying ultrasonic energy to the coupling fluid.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/411,076 filed on Mar. 25, 2009, the entire contents of which areincorporated herein by reference.

FIELD

The present patent application relates to methods for curing polymericmaterials and, more particularly, to methods for curing polymeric resinsusing ultrasound, wherein the cured resins are useful for bonding and/orfor the formation of various articles, including composite materials.

BACKGROUND

Synthetic resins, such as epoxy resins, polyester resins and the like,are commonly used as adhesives for bonding two substrates together.However, synthetic resins are also combined with appropriate substrates,such as fibers, glass, metals and wood, to form composite materials.Such composite materials find application in a variety of fields andindustries. For example, synthetic resin-based composite materials areused in the aerospace industry to form parts, propellers, tails, wingsand fuselages.

Composite materials typically are formed by preparing the syntheticresin (e.g., mixing a polymer with a catalyst), combining the substratewith the synthetic resin, molding the substrate and resin mixture intothe desired shape, and curing the molded substrate and resin mixtureuntil it achieves the desired physical properties. Once cured, theresulting composite material may be removed from the mold, at whichpoint it is ready for use, packaging or further processing.

Common molding techniques include vacuum bag molding, pressure bagmolding and autoclave molding. In vacuum bag molding, a mold or form,such as a two-sided mold, is filled with the substrate and resin mixtureand placed into a vacuum bag. Then, a vacuum is drawn in the vacuum bagto urge the substrate and resin mixture into the various nooks andcrannies of the mold. The vacuum bag is then sealed and cured.

Various techniques have been presented for curing synthetic resin. Mostcommonly, heat is used to cure resins. For example, sealed vacuum bagsmay be cured in an oven for a predetermined amount of time. However,alternative techniques for curing synthetic resins include theapplication of high pressure, whether alone or in combination with heat,as well as exposure to ultraviolet light.

Despite the advances in the field of synthetic resin curing andcomposite material formation, those skilled in the art continue to seeknew techniques for curing synthetic resins and forming compositematerials.

SUMMARY

In one aspect, the disclosed method for curing a resin may include thesteps of positioning the resin in a gaseous coupling fluid and applyingultrasonic energy to the gaseous coupling fluid until the resin becomesa solid mass.

In another aspect, the disclosed method for curing a resin may includethe steps of placing the resin into an appropriate reaction vessel,drawing a vacuum in the reaction vessel, positioning the vacuumedreaction vessel in a gaseous coupling fluid, and applying ultrasonicenergy to the gaseous coupling fluid.

In another aspect, the disclosed method for curing resins may includethe steps of placing an epoxy resin into an appropriate vessel, such asa film pouch, the epoxy resin including a catalyst, sealing the vessel,positioning the sealed vessel in a gaseous coupling fluid, and applyingultrasonic energy to the gaseous coupling fluid at least until the epoxyresin becomes a solid mass.

In another aspect, the disclosed method for curing resins may includethe steps of placing an epoxy resin into a vacuum bag, the epoxy resinincluding a catalyst, placing a mold into the vacuum bag, drawing avacuum in the vacuum bag, sealing the vacuum bag, positioning the sealedvacuum bag in a gaseous coupling fluid, and applying ultrasonic energyto the gaseous coupling fluid at least until the epoxy resin becomes asolid mass.

Other aspects of the disclosed method for curing resin will becomeapparent from the following description, the accompanying drawings andthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an apparatus for curing resins inaccordance with an aspect of the disclosed method for curing resin; and

FIG. 2 is a flow chart illustrating a particular aspect of the disclosedmethod for curing resin.

DETAILED DESCRIPTION

The first observation of the effect of ultrasonics was the discovery in1894 by Sir John I. Thornycroft and Sydney W. Burnaby. Messrs.Thornycroft and Burnaby observed that severe vibrations caused theerosion of a ship's propeller, and that the erosion was attributable tothe formation and collapse of tiny bubbles that from at the propeller.Over the years, knowledge of ultrasound has grown. Today, the generationand use of ultrasonic energy is found in various applications.

Ultrasound (also referred to as “ultrasonic energy”) can be transmittedthrough any material possessing elastic character. For example, whenultrasonic energy is applied to a liquid, the molecules in the liquidvibrate. As the average distance between the molecules in the liquidexceeds the critical molecular distance that holds the liquid intact,the liquid breaks down forming bubbles that cavitate. These bubbles canbe filled with gas or vapor and occur in various fluids including water,organic solvents, biological fluids, liquid helium, molten metals andthe like.

It has been determined that the collapse (i.e., cavitation) ofultrasonically-formed bubbles results in localized temperatures as highas 5000° C. and pressures as high as 1000 atmospheres for a lifetime ofless than one microsecond. Thus, the cavitation of a fluid due toexposure to ultrasound results in a tremendous concentration oflocalized energy in an otherwise relatively cold fluid.

It has now been discovered that ultrasonic energy, and the phenomenaassociated therewith, can be used to cure various synthetic resins,which may ultimately be used in the formation of composite materials,adhesive bonding, and the repair of damaged composite materials. Indeed,when ultrasound is used to cure synthetic resins, it may eliminate theneed for heat and may also expedite the curing process relative to othercuring techniques.

As shown in FIG. 1, an apparatus for curing resins, generally designated10, may include a reaction vessel 12, an ultrasound transducer 14, agaseous coupling fluid 16 and a resin 18 (shown generally as a block).The resin 18 may be positioned in the reaction vessel 12 and thereaction vessel 12 may be positioned in the gaseous coupling fluid 16such that ultrasonic energy may pass from the ultrasound transducer 14,through the gaseous coupling fluid 16 and to the resin 18 in thereaction vessel 12, thereby curing the resin 12 therein.

The resin 18 may be any synthetic resin capable of being cured uponexposure to ultrasonic energy for a certain amount of time. Optionally,the resin 18 may include a catalyst 20 (shown generally as a block),such as a curing agent or hardener, to facilitate or promote the curingprocess. In one aspect, the resin 18 may be an epoxy resin. One exampleof an appropriate epoxy resin is HYSOL® EA 956 epoxy resin availablefrom Henkel Corporation of Bay Point, Calif., which is a two-componentepoxy resin (i.e., it includes a catalyst 20). Another example of anappropriate epoxy resin is EPOFIX resin available from Struers A/S ofBallerup, Denmark, which is a two liquid system that includes both aresin and a hardener (i.e., a catalyst 20).

Optionally, the resin 18 may be combined with one or more substrates(not shown), such as fibers, glass, metals and wood, to form a compositematerial. The substrate may be selected based upon the intended use ofthe composite material. For example, the substrate may be used toreinforce the composite material or may be used to impart certaindesired physical properties to the composite material (e.g., thermalconductivity). Those skilled in the art will appreciate that, dependingon the desired result and/or the type of substrate used, the substratemay be dispersed in the resin, the resin may impregnate the substrate,or some other resin/substrate configuration may be used.

The gaseous coupling fluid 16 may be any gas capable of acousticallycoupling the ultrasound transducer 14 to the reaction vessel 12, andultimately to the resin 18 disposed therein. In one particular aspect,the gaseous coupling fluid 16 may be received in a vessel 22, such as atank or barrel. For example, the gaseous coupling fluid 16 may beambient air, nitrogen gas, argon gas or the like. Other examples ofuseful gaseous coupling fluids 16 will be readily apparent to thoseskilled in the art.

The temperature and pressure of the gaseous coupling fluid 16, as wellas other physical conditions of the gaseous coupling fluid 16, may be atambient conditions (e.g., 25° C. and 1 atm), thereby eliminating theneed for ovens, pressure vessels, autoclaves and the like. However,those skilled in the art will appreciate that the physical conditions ofthe gaseous coupling fluid 16 may be controlled as desired withoutdeparting from the scope of the present disclosure. Optionally, thephysical conditions of the coupling fluid 16 may be dictated by the typeof resin 18 being cured.

The ultrasound transducer 14 may be any device capable of generatingultrasonic energy. In one aspect, the ultrasound transducer 14 maygenerate ultrasonic energy in the range of about 20 to about 40 kHz. Forexample, the ultrasound transducer 14 may be of the type found in acommon ultrasonic cleaner, such as a typical ultrasonic jewelry cleanerhaving an integral couplant vessel. In another aspect, the ultrasoundtransducer 14 may generate ultrasonic energy in excess of 40 kHz.

As shown in FIG. 1, the ultrasound transducer 14 may be in directacoustical contact with the gaseous coupling fluid 16. For example, theultrasound transducer 14 may be an ultrasonic horn (e.g., a titaniumhorn) that has been directly immersed in the gaseous gaseous couplingfluid 16. Alternatively, an intermediate coupling agent may be disposedbetween the ultrasound transducer 14 and the gaseous coupling fluid 16.

The reaction vessel 12 may be any appropriate vessel capable oftransmitting ultrasonic energy from the gaseous coupling fluid 16 to theresin 18 received therein, while essentially isolating the resin 18 fromthe gaseous coupling fluid 16. In one exemplary aspect, the reactionvessel 12 may be a vacuum bag, wherein the resin 18 may be received inthe vacuum bag and ambient air may be evacuated from the vacuum bag.

Optionally, as shown in FIG. 1, a mold 24, such as a two-piece ortwo-sided mold, may be positioned in the reaction vessel 12 with theresin 18. Then, by drawing a vacuum in the reaction vessel 12, the resin18 may be urged into the mold 24 and, when cured, may conform to theshape of the mold 24. Those skilled in the art will appreciate thetechniques other than vacuum molding may also be used with the apparatus10 without departing from the scope of the present disclosure.

Referring now to FIGS. 1 and 2, one aspect of the disclosed method forcuring resin, generally designated 100, begins at block 102 by placingthe resin 18 into the reaction vessel 12 (e.g., a vacuum bag).Optionally, the resin 18 may be premixed with a catalyst 20 or thecatalyst 20 may be introduced separately and mixed in the reactionvessel 12. If the resin 18 is to be molded, a mold 24 may be placed inthe reaction vessel 12, as shown in block 104. Then, a vacuum may bedrawn in the reaction vessel 12 (block 106) and the reaction vessel 12may be sealed (block 108) to maintain the vacuum. As shown in block 110,the sealed reaction vessel 12 may be positioned (e.g., immersed orsupported by a structure) in the gaseous coupling fluid 16 and theultrasound transducer 14 may be actuated (block 112) to apply ultrasonicenergy to the resin 18 to cure the resin 18. The application ofultrasonic energy may continue until the resin 18 is completely cured orat least forms a solid mass.

Accordingly, the curing of resins, such as epoxy resins, may be obtainedby placing the a resin in an ultrasonic field to receive ultrasonicenergy. Of particular interest, a complete resin cure may be obtainedfaster when ultrasonic energy is used.

Although various aspects of the disclosed method for curing resin havebeen shown and described, modifications may occur to those skilled inthe art upon reading the specification. The present application includessuch modifications and is limited only by the scope of the claims.

What is claimed is:
 1. A method for processing resin, comprising causingcavitation of a gaseous coupling fluid at ambient temperature andatmospheric pressure in which resin is disposed.
 2. The method of claim1 wherein said causing further comprises applying ultrasonic energy tothe coupling fluid.
 3. The method of claim 1 wherein said causingfurther comprises causing cavitation of a coupling fluid includingambient air.
 4. The method of claim 1 wherein said causing furthercomprises causing cavitation of the coupling fluid such that the resinis cured.
 5. The method of claim 1 wherein said causing furthercomprises causing cavitation of the coupling fluid in which resinincluding a substrate is disposed.
 6. The method of claim 5 wherein saidcausing further comprises causing cavitation of the coupling fluid suchthat a composite material is formed from the resin.
 7. The method ofclaim 5 wherein said causing further comprises causing cavitation of thecoupling fluid such that adhesive bonding of the resin occurs.
 8. Themethod of claim 1 wherein the resin is an epoxy resin including acatalyst.
 9. The method of claim 6 wherein the composite materialcomprises the substrate dispersed in the resin.